The present application relates generally to solar energy modules and, more particularly, to a backskin material to protect and seal solar cells.
Solar energy modules include solar cells (also known as photovoltaic cells) for generating electricity from sunlight. The most common type of solar cell is a crystalline silicon solar cell. Other types of solar cells are based on thin film technology. Thin film solar cells can be made, e.g., from amorphous silicon (α-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (GIGS). Other types of solar cells include cells that are made from polymers, so-called dye sensitized cells, and nano particles.
Crystalline silicon solar cell modules as well as many thin film modules have a sheet of glass on the light receiving side (i.e., front side) and a polymeric sheet on the back side of the module. The polymeric sheet on the back side of the module is usually termed the backskin.
A widely used backskin is a three layered laminate utilizing a vinyl fluoride film such as Tedlar® (a trademark of E.I. DuPont de Nemours and Company, Wilmington, Del.) as an outer layer of the three layers. The outer layer is generally on the order of about 1 to 2 mils thick. The center layer of this type of conventional backskin material is usually formed from a layer of polyethylene terephthalate (PET), and is typically about 6 to 8 mils thick. Examples of materials utilized for the formation of the inner layer include Tedlar® and ethylene vinyl acetate (EVA).
Components of photovoltaic modules can be subjected to qualification requirements established by Underwriters Laboratories (UL) of Northbrook, Ill. for meeting certain electrical and mechanical characteristics. In particular, photovoltaic modules and their components are tested to determine their Relative Thermal Index (RTI). The RTI is a measure of the creep resistance of a material at high temperatures. Materials in a photovoltaic module have a minimum temperature requirement of 90° C. and typically are subjected to temperatures as high as about 150° C. during testing.